Magnetic Random Access Memory (MRAM) technology utilizes storage cells, for example, magnetic tunnel junctions (MTJs), which generally each have at least two magnetic regions or layers with an electrically insulating barrier layer between them. The data storage mechanism relies on the relative orientation of the magnetization of the two layers, and on the ability to discern this orientation through electrodes attached to these layers. For background, reference is made to U.S. Pat. Nos. 5,650,958 and 5,640,343 issued to Gallagher et al. on Jul. 22, 1997 and Jun. 17, 1997, respectively, which are incorporated herein by reference.
Typically, each storage cell includes a magnetically changeable (reversible) or “free” region and a proximate magnetically referenced “fixed” region arranged into a MTJ. A storage cell can be written by reversing the free region magnetization using applied bi-directional electrical and resultant magnetic stimuli via its respective bit line and word line. The storage cell can later be read by measuring the resultant tunneling resistance between the bit line and word line, which assumes one of two values depending on the relative orientation of the magnetization of the free region with respect to the fixed region.
MRAM arrays typically include an array of data storage cells respectively positioned at intersections of word lines and bit lines. When writing storage cells, it is desirable to write only selected storage cells in the array, without affecting other non-selected cells. However, the magnetic fields generated from the bit and word line during writing can disturb the magnetization state of adjacent non-selected cells, thereby reducing reliability of the array. In addition, the magnetic state of a cell can be affected by the magnetization state of adjacent cells, especially in a dense array.
Accordingly, a need exists for improving the write selectivity of memory storage cells within a memory array.